The invention relates to a hybrid drive and, more particularly, to a hybrid drive for a motor vehicle, comprising an internal combustion engine which is connected via a clutch and a gearbox to a drive shaft. A three-phase machine is fed by a three-phase converter.
Hybrid drives with a comparable parallel arrangement, in which the torques of an internal combustion engine and an electrical machine are added together in the gearbox, are known from German Patent document DE 28 05 594 A1, the Swiss Journal: Technische Rundschau No. 46, 15.11.1983, page 9, and from the post-published German Patent document DE 40 41 117 A1, corresponding to European Patent Document EP 0492152. These known drives are distinguished by the fact that the conventional drive train is retained almost unaltered while eliminating the starter and the generator. The starter and generator functions are assumed by the electrical machine coupled to the gearbox, which can be used both as a generator for charging an electric energy accumulator and as a motor for driving the vehicle.
Since, in the past, commutator machines were generally provided as electrical driving machines for hybrid drive arrangements, it was necessary to ensure when designing the drive that the electrical commutator machine could be mechanically separated from the drive train when the drive was being provided exclusively by the internal combustion engine. The reasons for doing this are, on the one hand, the friction torque caused by the commutator and on the other hand, the limited life of the commutator due to mechanical wear. In such drive arrangements, the commutator machine was generally separated by means of a mechanical clutch and/or the brushes were raised from the commutator by means of an additional mechanical device. Also provided in each of the above-mentioned publications is at least one separating clutch, by which the electrical machine can be separated from the drive train.
The advance of semiconductor technology has made it possible, instead of commutator machines, to use a three-phase machine in which no electrical contact is necessary between the stator and the rotor. For example, an asynchronous machine with a squirrel cage rotor or a permanently excited synchronous machine can be used. The rotating field revolving in the air gap during operation with the motor and forming a torque is produced by a semiconductor three-phase converter. Since there is no electrical contact in such an electrical machine, the rotor can be permanently connected mechanically to the internal combustion engine driven drive train since, as long as the three-phase converter is electrically inhibited, the part exerts no reaction on the mechanical part of the drive apart from the negligible bearing friction. This idea is adopted in a different type of hybrid drive, those with serial arrangement, as described in German Patent documents DE 29 43 554 A1 and DE 37 37 192 A1. The internal combustion engine and the three-phase machine are here arranged in series on the drive train. Together with components of a first separating clutch on the internal combustion engine side and components of a second separating clutch on the gearbox side, the rotor of the three-phase machine forms a centrifugal mass which can be coupled to the internal combustion engine. A disadvantage of the serial arrangement is considered to be the fact that an extension in the axial direction between the internal combustion engine and the gearbox generally requires major structural modifications in a vehicle and therefore also requires an extremely compact design of the three-phase machine in the axial direction.
An object of the invention is based is to design a hybrid drive of the generic type in such a manner that both parts of the drive can be of essentially conventional design and that as great as possible a savings of mechanical components is achieved.
This object is achieved according to the present invention by a hybrid drive for a motor vehicle, comprising an internal combustion engine which is connected via a clutch and a gearbox to a drive shaft. A three-phase machine is fed by a three-phase converter. A rotor of the three-phase machine is coupled in a continuous, mechanical manner to a layshaft of the gearbox. The power flow between the layshaft and the three-phase machine is determined solely by the electrical controlling of the three-phase machine.
The advantages, achieved by means of the invention, over the above-mentioned prior art consist, in particular, in the fact that a second separating clutch separating the three-phase machine from the drive train is eliminated. At the same time, the structural shape of the three-phase machine is not subject to any special restrictions. If it appears necessary, it is even possible in the case of the arrangement according to the present invention to connect the three-phase machine to the layshaft via a single gear stage with fixed transmission. The rated speed of the three-phase machine can be increased in accordance with this mechanical transmission ratio, with the result that the machine becomes smaller for the same power.
It is furthermore apparent that in the case of operation where both the internal combustion engine and the three phase machine are contributing to the drive, i.e. to cover the peak load during overtaking maneuvers for example, the arrangement according to the present invention proves to be particularly advantageous since the mechanical driving torques are added in the layshaft of the gearbox. Unlike in the case of a serial arrangement, the shaft of the three-phase machine can be dimensioned merely for its own torque and can therefore be of a weaker design.
The present invention, in one embodiment, envisages a controlling of a three-phase converter in accordance with the known, prior-art rules for three-phase drives fed by current converters in vehicles. Accordingly, the three-phase machine, under the control of the accelerator pedal, can produce its rated torque or an optionally briefly permissible overload torque from standstill to the rated speed. As a further advantage there is the fact that both an electric starter motor for the internal combustion engine and a generator can be dispensed with since the function of both machines is assumed by the three-phase machine: when the mechanical gearbox is in the neutral position, the internal combustion engine can, with-the clutch between the internal combustion engine and the gearbox closed, be run up in a speed-controlled manner by the three-phase machine, directly from the traction battery via the three-phase converter. As soon as the internal combustion engine has reached the rotational speed for ignition, it is possible for the traction battery to be charged by the internal combustion engine simply by switching over the power flow in the three-phase converter.
Further embodiments of the present invention are described by means of which gearbox shift operations are assisted by the three-phase machine. Thus, during a gear change, the controlling of the three-phase machine can be influenced in a manner such that the mechanical synchronization means which are intended to achieve, in a mechanical way by frictional engagement, the synchronism of the gear pairs to be coupled in the gear box, have virtually no frictional work to perform since the torque for decelerating the transmission parts when shifting to a higher gear stage and for accelerating the transmission parts when shifting to a lower gear stage is provided by the three-phase machine. On the one hand, it is thereby possible to improve the gearbox shift operations by shortening the unwanted interruption in the tractive effort and, on the other hand, it is even possible to conceive of a reduction in the dimensions of the mechanical synchronization means relieved by the electric synchronization aid or, in the case of a further embodiment, of dispensing with these completely. In both cases, the mechanical outlay in the gearbox is reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.